Certain diseases of the respiratory tract are known to respond to treatment by the direct application of therapeutic agents. As these agents are most readily available in dry powdered form, their application is most conveniently accomplished by inhaling the powdered material through the nose or mouth. This powdered form results in the better utilization of the medicament in that the drug is deposited exactly at the site desired and where its action may be required; hence, very minute doses of the drug are often equally as efficacious as larger doses administered by other means, with a consequent marked reduction in the incidence of undesired side effects and medicament cost. Alternatively, the drug in this form may be used for treatment of diseases other than those of the respiratory system. When the drug is deposited on the very large surface areas of the lungs, it may be very rapidly absorbed into the blood stream; hence, this method of application may take the place of administration by injection, tablet, or other conventional means.
It is the opinion of the pharmaceutical industry that the bioavailability of the drug is optimum when the drug particles delivered to the respiratory tract are between 1 to 5 microns in size. When the drug particles need to be in this size range the dry powder delivery system needs to address a number of issues:
(1) Small size particles may develop an electrostatic charge on themselves during manufacturing and storage. This may cause the particles to agglomerate or aggregate, resulting in clusters of particles which have an effective size greater than 5 microns. The probability of these large clusters making it to the deep lungs then decreases. This in turn results in a lower percentage of the packaged drug being available to the patient for absorption.
(2) The amount of active drug that needs to be delivered to the patient may be of the order of 10 s of micrograms. For example, in the case of albuterol, a drug used in asthma, this is usually 25 to 50 micrograms. Current manufacturing equipment can effectively deliver aliquots of drugs in milligram dose range with acceptable accuracy. So the standard practice is to mix the active drug with a filler or bulking agent such as lactose. This additive also makes the drug “easy to flow”. This filler is also called a carrier since the drug particles also stick to these particles through electrostatic or chemical bonds. These carrier particles are very much larger than the drug particles in size. The ability of the dry powder inhaler to separate drug from the carrier is an important performance parameter in the effectiveness of the design.
(3) Active drug particles with sizes greater than 5 microns will be deposited either in the mouth or throat. This introduces another level of uncertainty since the bioavailability and absorption of the drug in these locations is different from the lungs. Dry powder inhalers need to minimize the drug deposited in these locations to reduce the uncertainty associated with the bioavailability of the drug.
Prior art dry powder inhalers (DPIs) usually have a means for introducing the drug (active drug plus carrier) into a high velocity air stream. The high velocity air stream is used as the primary mechanism for breaking up the cluster of micronized particles or separating the drug particles from the carrier. Several inhalation devices useful for dispensing this powder form of medicament are known in the prior art. For example, in U.S. Pat. Nos. 3,507,277; 3,518,992; 3,635,219; 3,795,244; and 3,807,400, inhalation devices are disclosed having means for piercing of a capsule containing a powdered medicament, which upon inhalation is drawn out of the pierced capsule and into the user's mouth. Several of these patents disclose propeller means, which upon inhalation aid in dispensing the powder out of the capsule, so that it is not necessary to rely solely on the inhaled air to suction powder from the capsule. For example, in U.S. Pat. No. 2,517,482, a device is disclosed having a powder containing capsule placed in a lower chamber before inhalation, where it is pierced by manual depression of a piercing pin by the user. After piercing, inhalation is begun and the capsule is drawn into an upper chamber of the device where it moves about in all directions to cause a dispensing of powder through the pierced holes and into the inhaled air stream. U.S. Pat. No. 3,831,606 discloses an inhalation device having multiple piercing pins, propeller means, and a self-contained power source for operating the propeller means via external manual manipulation, so that upon inhalation the propeller means aids in dispensing the powder into the stream of inhaled air. See also U.S. Pat. Nos. 3,948,264 and 5,458,135.
In prior U.S. Pat. Nos. 7,318,434 and 7,334,577 incorporated herein by reference, and assigned to the common assignee MicroDose Therapeutx, Inc., there is provided an improvement over prior art inhalers that utilize vibration to facilitate suspension of power into an inhaled gas stream and which utilizes synthetic jetting to aerosolize drug powder from a blister pack or the like. As taught in the aforesaid U.S. Pat. Nos. 7,318,434 and 7,334,577 there is provided a dry powder inhaler having a first chamber such as a blister pack or other container, for and holding a dry powder, and a second chamber connected to the first chamber via a passageway for receiving an aerosolized form of the dry powder from the first chamber and for delivering the aerosolized dry powder to a user. A vibrator is coupled to the dry powder in the first chamber. The vibrator is energized and coupled to the first chamber and drives the powder from the chamber by synthetic jetting.
As described in U.S. Pat. No. 7,080,644 also incorporated herein by reference, and also assigned to common assignee MicroDose Therapeutx, Inc., controlled aliquots or doses of a medication or drug are pre-packaged in a blister pack, which includes a frangible crowned top element which may be conical, conical with a rounded point, rounded, or other raised shape configuration, and a bottom element which may be a flat web or membrane, or which itself may be of shaped configuration, e.g. conical, round, dish shaped, etc. for closely engaging with an underlying vibrating element, the shape and size of which is chosen to provide optimum controlled delivery of a given medication or drug. The top element of the blister pack is pierced with a piercing device such as a sharp needle to form one or more apertures for delivery of the medication or drug contained within the blister pack. The hole pattern and hole size is selected to provide optimization of delivery of the particular medication or drug packaged therein.